In general, a CZochralski (hereinafter, referred to as a “CZ”) method is most widely used as a method for manufacturing silicon wafers. In the CZ method, polycrystalline silicon is charged into a quartz crucible, and the charged polycrystalline silicon is heated and molten by graphite heater. Then, a seed crystal is immersed into the resultant molten silicon to cause crystallization on an interface therebetween. Thus, a monocrystalline silicon ingot is grown by pulling up the immersed seed crystal while rotating the seed crystal. Then, the grown silicon ingot is sliced, etched, and polished to manufacture a silicon wafer.
The monocrystalline silicon ingot or silicon wafer manufactured through the above-described processes may have crystal defects such as crystal originated particles (COPs), flow pattern defects (FPDs), oxygen induced stacking faults (OISFs), and bulk micro defects (BMDs), which are called grown-in defects. There is a need for reducing the density and size of the grown-in defects. There has been confirmed that the crystal defects affect the yield and quality of devices. Thus, it is very important to completely remove the crystal defects and to easily and quickly evaluate the crystal defects.
Also, according to the crystal growth conditions, the monocrystalline silicon ingot or silicon wafer includes a V-rich zone in which vacancy-type point defects are prevalent to cause supersaturated vacancy cluster (condensed) detects, a Pv zone in which vacancy-type point defects are prevalent, but no cluster defects exist, a vacancy/interstitial (V/I) boundary, a Pi zone in which interstitial point defects are prevalent, but no cluster defects exist, an I-rich zone in which interstitial point defects are prevalent to cause supersaturated interstitial cluster defects.
Also, it is important in evaluation of the quality level of the crystal to confirm how the above zones are changed depending on their occurrence positions and crystal lengths of the monocrystalline silicon ingot.
According to the related art, in the monocrystalline silicon ingot manufactured using the CZ method, if the monocrystalline silicon ingot is grown (fast growth) above a V/G critical value according to a boron-copper theory that is called a V/G, a V-rich having void defects occurs. Also, if the monocrystalline silicon ingot is grown (slow growth) below the V/G critical value, oxygen induced stacking faults (OISFs) occur in an edge or center zone into a ring shape. If the monocrystalline silicon ingot is more slowly grown, a dislocation loop in which interstitial silicon is gathered is tangled to cause an I-rich that is a loop dominant point (LDP) defect zone.
A perfection zone, but not a V-rich or an I-rich, exists on a boundary between a V zone and an I zone. The perfection zone may be classified into a Pv zone that is a vacancy dominant point (VDP) perfection zone and a Pi zone that is an interstitial dominant point (IDP) perfection zone. To manufacturing perfection wafers, the above zones may be recognized as a manufacturing margin.
Methods for evaluating a silicon wafer according to the related art are as follows.
First, there is a method for evaluating silicon wafer surface defects which performs an RTP processing on a wafer where a COP defect having a size less than about 65 nm exists to calculate a diffusion distance of a minority carrier on the wafer using a surface photovoltage (SPV) method. Here, a COP serves as a recombination center of the minority carrier. Thus, the COP which is not detected by a particle counter may be detected.
However, in case of the SPV method using the RTP processing, even though a crystal defect having a size of about 65 nm or less can be detected, an existing particle counter may detect only a crystal defect and distribution having a size of about 50 nm or less or a size of about 20 nm to about 30 nm. Thus, a more precise measurement method is required.
Second, there is a method which detects a zone, which has improved time zero dielectric breakdown (TZDB) properties and is not included in a V-rich zone, an OISF zone, and a zone which is detected by a Cu decoration method, a reactive ion etching (RIE) method. When RIE defects are not detected through the RIE method, the RIE method may be a method for confirming a high quality silicon wafer where oxidation layer breakdown properties are not degraded even though a device is manufactured.
Although the RIE method is advantageous for detecting a TZDB degradation zone, equipment for performing a separate ion etching process should be provided. In addition, separate equipment for confirming a wafer (that is an actual product) in which the RIE process is performed should be provided.
Third, there is a method which can confirm the crystal degradation zone, which is not confirmed through the second method, by improving the TZDB method. Although the existing TXDB method may be improved to confirm the RIE zone, additional thermal process and annealing processes may be required. Thus, it takes a long time to perform the above-described method, and also, sample manufacturing fail possibility may exist when a sample for measuring the TZDB is manufactured.
Fourth, in a method for classifying crystal defect zones of the monocrystalline silicon and a Cu contamination solution for evaluating the crystal defect zones, one side surface of the wafer may be contaminated using the Cu solution having a predetermined concentration, and then the wafer may be thermally processed at a specific temperature and for a predetermined time to visually observe a Cu haze occurring in a specific zone, thereby classifying the crystal defect zones.
Although the Cu haze evaluation method has an advantage in which the Cu haze evaluation method can confirm other crystal defect zones in addition to the TZDB degradation zone, an accurate Cu concentration level should be maintained. In addition, separate two thermal processing processes should be performed for confirming an accurate crystal zone, for example, the TZDB degradation zone or the RIE detection zone.